For millennia people have been contemplating ways to harvest and/or produce fluid flow for numerous uses, for example, from grinding flour to human flight. Whether one is producing fluid flow, for example, for flight, or harvesting fluid flow, for example, to move a vessel across a lake, the principles used are similar.
Depending upon the type of fluid, the application, and the space available for the application, different types of devices have been employed for harvesting and/or producing fluid flow. For example, sailboats are some of the earliest and most efficient vessels that have harvested wind flow for travel. By employing large sails, the boat makers are able to harvest large areas of flowing air. The shear volume of captured energy provides plenty of thrust, even at fairly low wind speeds. Sails are designed to make good use of the available space in a watercraft and can be quite efficient given the space limitations.
Since density of water is higher than that of air, boat makers have resorted to devices such as propellers for low-volume, high speed applications in watercraft. Even though the surface area available on a propeller might be much smaller than that of a sail, the high rotational speed of the propeller against a higher density fluid makes for an efficient fluid flow mechanism.
Larger blades have also been employed for providing flow in fluids such as water. One example is a paddlewheel. Paddlewheels provide for a large surface area and can be efficient fluid movers like sails. However, since paddlewheels are rotated in a rotational direction generally perpendicular to the water flow, they cannot be fully submersed in water in order to operate properly. The design of a paddlewheel makes it an efficient fluid flow device when the paddlewheel is about halfway or more out of the water. In this manner, the paddlewheel is able to take advantage of the difference in densities between water and air in moving a watercraft in the desired direction. If a paddlewheel is fully submerged in water, the paddlewheel will tend to drive the water in a circle rather than transforming the rotational movement into translational movement.
A downside of most fluid harvesting and/or producing devices is less than ideal efficiency. For example, in applications such as wind harvesting, using devices such as conventional propellers has the disadvantage of reduced surface area available for harvesting energy. However, smaller propeller blades are used so as not to reduce the overall fluid flow by deflecting it off the blades in other directions. Using devices with larger surface areas, such as conventional turbines, also has disadvantages. Although turbines can be more efficient than propellers in certain fluid flow applications because they can reduce the deflection issues that remain prevalent in wind harvesting mechanisms, turbines typically have the disadvantage of additional friction produced from having more surface area moving at an angle to fluid flow (i.e., more drag).
Pumps are devices that typically produce fluid flow within a housing. Pumps typically draw in a fluid through an inlet on the housing and expel the fluid through an outlet on the housing. Certain pumps are positive displacement pumps. Positive displacement pumps expel a given volume of fluid per cycle of the pump at a given displacement setting of the pump. Certain positive displacement pumps are variable displacement pumps that can be set at a range of displacement settings. Other positive displacement pumps are fixed displacement pumps that have a fixed displacement setting. Certain pumps are rotodynamic pumps in which kinetic energy is added to the fluid by increasing the flow velocity. This increase in kinetic energy can be converted to potential energy (i.e., pressure) when the fluid flow velocity is reduced. Rotodynamic pumps are not typically positive displacement pumps.
Improvements in fluid flow devices are desired. Optimizing speed and torque of the devices by making optimal uses of space and flow direction are important. Maximizing flow area usage, minimizing friction through flow direction matching, and the ability to provide full fluid submersion without creating circular/counter-flow are desired.